A fluid evolutive product is a liquid in which a reaction resulting in a physical or chemical transformation takes place such as producing a solid phase or modifying the characteristics of a solid phase initially carried by the liquid.
The present invention is concerned with manufacturing of board by pouring, upon a moving conveyor, a fluid evolutive product. Plaster powder and water mixture is exemplary of such a product. As soon as plaster powder is mixed with water, it starts evolving rapidly until it sets completely. Continuous process manufacturing of plaster building components demands a control of the plaster reacting stage at each moment and at all stages of mixing, from the initial supplying of pulverized plaster powder and water up to the end of line where completed building components are ready to be used.
When an evolutive product has a pasty consistency, the way to control its evolution inside a tooth type mixer is known, and the way to spread it in continuous process upon a moving conveyor having a conveyor belt in order to form a more or less even plaster strip which may be put into forms in a continuous process is known. But working with a paste necessitates heavy equipment since the cohesive forces to be overcome are important, and paste flow rate regulation and paste level measurement are far from accurate. Hence there is unevenness in the amount of the product supplied to the moving conveyor and consequently unevenness in the finished product quality.
When the evolutive product has a liquid consistency, as in the case of plaster, the only way known to use it for the manufacturing of building components is in a noncontinuous process. It is poured into molds where it is left until the plaster sets. Up to now, a liquid plaster mixture is not used in a continuous process, partly owing to the difficulty encountered in holding liquid plaster by a valve during its mixing inside a standard mixer without the mass setting of deposits at the level of the narrow channel created by the valve, and partly also owing to the difficulty encountered in keeping an evolutive product such as plaster in a continuous process pouring facility without any premature mass setting of the plaster inside the facility. The applicants are the first to develop the flow rate regulating of a plaster fluid mixture coming out of a mixer. In this connection reference may be had to our copending applications entitled "Process and Mechanism for Evolutive Pulp Flow Regulation" U.S. patent application Ser. No. 3,415, now U.S. Pat. No. 4,334,786 and "Continuous Process Mixing of Pulverized Solids and Liquids and Mixing Apparatus" U.S. patent application Ser. No. 3,416, now U.S. Pat. No. 4,257,710 issued Mar. 24, 1981, filed concurrently herewith on Jan. 15, 1979, and incorporated herein by reference.
Being able to control the time of stay of a fluid evolutive product in a mixer, such as a liquid plaster powder and water mixture, through runoff flow rate regulation of said mixture coming out of the mixer, applicants then sought the use in continuous process of such a liquid mixture for building panel manufacturing in such a way as to make use of the advantages inherent in the use of a liquid, i.e., level detection accuracy, more even spreading of mixture and lighter equipment.
The way to pour out a product upon a moving bed, and to let it spread out by itself is known, the thickness of plates thus manufactured being a function of bed running speed. But when working with a fluid evolutive product, it is difficult to control its spreading and difficulties are encountered in thick plate manufacturing. In order to limit and control spreading, it is possible to consider making use of devices habitually relied upon to pour non-evolutive products. They generally comprise a bottomless container placed above a moving conveyor with a slit formed by said conveyor and by the lower edge of the plate which forms the downstream wall of the container.
The container is filled with product, thus creating a storage load above the conveyor and the product runs off on the conveyor through the slit at the base of the container. If a plaster powder and water mixture were poured in such a device, it would set, first along the container's walls and then on the slit edges and the pouring facility would soon become blocked up.
The board manufacturing process involving pouring upon a moving conveyor an evolutive fluid product, such as a plaster powder and water mixture, which is the object of the invention, avoids such blocking up.